As is now well established in the art, the blade, as the hockey stick's striking surface, is a part submitted to extreme load conditions during shots like a slap shot, for example. The blade may be submitted to impact, torsion, bending, tension and shearing forces.
Current methods of making hockey stick blades tend to meet requirements resulting from such a range of forces to which the blades are submitted, by resorting to different types of structures, including for example, monobloc structures, sandwich structures and reinforced structures. Such methods yield blades having a weight essentially proportionate to the respective weight of the materials used, and usually fail to provide an optimized combination of minimum weight and maximum stiffness/strength.
For example, in the case of sandwich-type blades, a main weakness and a reduced service life are related to a non-satisfactory quality of the joining step or of the gluing step between a core and outer walls, thus resulting in a tendency to delaminate, peel or tear. As soon as peeling initiates, for example, the mechanical properties of the blade as a whole are reduced, thereby jeopardizing the quality of the hockey stick itself.
Efforts to optimize a long-term strength of sandwich-type blades have involved using braids around the core of the sandwich structure, which results in an effective increase of strength and life limit of so-called high-performance blades.
A method of fabricating such a high performance blade standardly comprises providing two longitudinal semi-cores made in foam, pulling on each semi-core a generally tubular jacket made of reinforcing fibers, pulling a third generally tubular jacket made of reinforcing fibers on the two semi-cores individually wrapped and located longitudinally side-by-side, and impregnating a resulting assembly with resin, thereby yielding a sandwich-type beam comprising a full core extending from a first edge to a second edge thereof across the whole width thereof. Then, a molding step yields a blade, the performances of which depend on the quality of the assembly between the two semi-cores and on an adhesion quality between the two semi-core assembly and outer walls. Such method may be found described in U.S. Pat. No. 6,918,847 issued Jul. 17, 2005 to Gans.
The above efforts still fail as far as the weight problem is concerned. A minimized weight is all the more critical since synthetic fibers now allow making increasingly light synthetic fibers shafts for hockey sticks. It has been noted that assembling a light shaft and a relatively heavy blade results in an unbalanced hockey stick, which is unacceptable in the field of high-performance hockey.
Therefore, there is need in the art for a hockey stick blade obviating the current drawbacks.
Conventional molding techniques used to fabricate composite blade for hockey stick comprising a core made of foam reinforced with layers of fibers of carbon, kevlar, polyethylene or glass are in general obtained by a close-mold process.
The pre-assembly of “the foam insert—reinforcing fibers” having the general shape of a straight hockey stick blade is positioned inside a two-part mold in which, in a second step, a liquid polymeric resin is injected under pressure and or vacuum. Under injection pressure and/or vacuum, the liquid resin will impregnate the entire pre-assembly of foam-carbon fibers and solidify after under chemical reaction, commonly called polymerization or cross-linking. The negative particularity of such molding technology is the fact that, when the pre-assembly of the foam insert around which the carbon fiber cloth or braid is positioned inside the cavity portion of the mold, there is no specific fiber strengthening or specific fiber alignment. The dry fiber clothe or braid is relatively loose and it is in this state that it will be resin impregnated after mold closing and resin injection, thus generating wrinkles, for example, and non uniform adherence with the foam core. Such situation results in a molded blade in which the continuous reinforcing fibers are not well aligned and relatively misoriented inside the solidified resin matrix.
The same situation exists when molders use “prepreg” instead of dry reinforcement. Prepreg is a form of material combining, in a semi-solidified state, fiber reinforcement and resin matrix, ready to mold only under pressure and heat in a close-mold process.
In this particular case, the fiber-braided envelope will be slid over the foam cores assembly and, after mold closing under pressure, only heat will be applied to solidify the blade assembly.
When, in use, the molded blade is put under stress, such as during a slap shot or equivalent, the not well aligned and/or not-straightened reinforcing fibers are not reacting instantaneously to generate the optimum or acceleration or impulse to the puck.
Under the striking or impact energy generated by the player, the molded blade will, in that particular situation, deflect more prior to absorb energy and finally react with less speed to kick the puck at the speed anticipated.
Therefore, molding hockey stick blades according to the conventional close-mold technology does not generate an optimum stiffness, which is a main factor required to totally convert the induced energy by the player into puck speed.
The extra blade deflection, when subjected to load and due to carbon fiber molded state (unstraightened and misoriented), is a serious handicap to optimize puck speed in a slap shot, for example.